1. Field of the Invention
The present invention relates generally to the art of glass melting, and more particularly to improvements in supplying combustion air to the regenerators of a regenerative tank-type glass melting furnace.
2. Description of the Prior Art
As is well known, flat glass is produced in a continuous tank-type melting furnace, wherein raw batch materials are continuously delivered to the charging end of the furnace, melted and refined as they move through the furnace, and then withdrawn from its delivery end as a continuous ribbon. In furnaces of this type, heat for melting the raw batch materials is provided by a series of ports arranged along each opposed longitudinal side wall, the ports leading to sources of supply of fuel and preheated combustion air. The combustion air is preheated by contact with the refractory bricks heated by the hot waste gases which have previously passed through the checkerwork of the regenerators opposite the ports being fired. The direction of firing is periodically reversed, that is, the two series of ports are alternately operated so that first one series of ports is fired and the opposite series exhausts the hot waste gases. Then at periodic intervals of about 20 to 30 minutes, the operating condition of the two series of ports is reversed; that is, the ports previously being fired serve as the exhaust ports and the ports exhausting the hot waste gases serve as firing ports.
Conventionally, the combustion air is admitted to the upstream end of the regenerators, i.e. the end adjacent the charging end of the furnace, through tunnels extending the length of and lying beneath the checkerwork structure of the regenerators. It has been found that although the tunnels extend throughout the entire length of the regenerators on each side of the furnace, because of their flow characteristics, withdrawal of hot exhaust gases is predominantly through the upstream end of the regenerators. Conversely, when colder combustion air is admitted to the regenerators, it is driven predominantly to the downstream end. Thus, the tendency to create a temperature differential is compounded and, as a result, a temperature gradient is established within the checkerwork of the regenerators whereby the checkerwork temperature at the upstream end; that is, in the vicinity of the first port, is considerably higher than at the downstream end. This is believed to not only reduce the thermal efficiency of the furnace, but also to result in premature deterioration of the regenerators due to the abnormally high localized temperatures. In other words, because of the abnormally high localized temperatures and concentration of the stored heat in localized areas, the efficiency with which the combustion air is preheated during the firing cycle is reduced.